The invention is related to a method and apparatus for protecting components of electrical or electronic systems from being damaged due to overheating of thermally degradable materials, including electronic components and wiring insulation. More generally, the invention is also useful to monitor and indicate overheating conditions that may occur in non-electrical systems. In addition to providing a very sensitive indication of destructively high temperature levels in a monitored system, the invention provides a practical means for readily localizing the areas of a monitored system where overheating has occurred. More particularly, in certain arrangements of the invention, such a localizing function is achieved by using different perfluorocarbon tracers (PFTs) to monitor discrete portions of a system. Such PFTs are mixed and formed into suitable carrier compounds, such as compounds that result form mixing predetermined volumes of PFTs with selected volumes of insulating paints, elastomeric films, or polymeric support materials, which can then be readily applied to form insulating and thermal monitoring coatings around electrical wiring or electronic components of a system. In the operation of such a monitored system, when the system is in a normal temperature range the PFTs remain trapped within the carrier materials of the carrier compositions, but when predetermined portions of the wiring or coated components become overheated such overheating causes an unusually high level of PFT vapor to be emitted from the compositions into the surrounding environment. To complete the monitoring system, one or more conventional PFT detectors are positioned in that ambient environment and are selected to be operable to indicate the type of PFTs that are emitted from given sections of wiring or from a given coated component, thereby to identify and localize the overheated portion of the system.
The problems associated with undesirable overheating of electrical insulation or other portions of electrical systems or other apparatus are common and long standing ones. These problems are particularly common in electrical or electronic systems that are subjected to unregulated overcurrent conditions, and that also susceptible to insulation breakdown and failure due to normal aging of the constituents of the insulating compositions used in the systems. For example, it is well known in the prior art to provide a wide variety of thermal breakdown indicators for monitoring electrical apparatus or components that are covered with protective coatings subject to such breakdown. Such prior art systems typically use thermoparticulating materials that breakdown into small flakes or particles, such as smoke particles, when certain pre-determined temperatures are exceeded within a coated component or apparatus. Examples of such particulating over-heat indicator compositions are shown in U.S. Pat. Nos. 4, 179,926 and 4,151,746. Those patents also describe use of the compositions in a manner such that they provide means for indicating the relative location within a system of a coating in which overheating has occurred.
Such thermo-particulating indicating systems have several disadvantages relative to indicators that emit essentially a particulate free and essentially a gaseous vapor at predetermined temperatures. Particulates evolved from such prior art indicator compositions are not transported as efficiently as gas vapors in the ambient gas stream around the monitored components or apparatus. Because such particulates are heavier than the ambient gases, they settle out of the gases and thus often do not reach associated monitoring detectors in the same efficient concentrations that are realizable with a gaseous-vapor overheat indicator. Moreover, the types of detectors used with such thermo-particulate indicator systems are normally either ion chamber detectors, such as those used in conventional household smoke detectors, or they may be condensation nucleic counters, which cannot discriminate between the type of thermo-particulate used as an indicator and any other particulate that may be in the ambient, such as dust particles or smoke from sources other than the monitored electrical apparatus. Thus false readings or undesired indications are often obtained from such particulate indicators.
For certain narrow fields of application, such as use within the hydrogen cooling systems of electrical generators of the type described in the two above-mentioned patents, the ambient system within the containment housings is not so susceptible to producing misleading indications, because no dust or random ambient particles are permitted within such hermetically sealed cooling systems. However, that susceptibility of the particulate-type of indicators to produce false or misleading readings, caused by particulates introduced into the ambient from sources beyond the monitored system, would be a significant detriment if such indicators were to be applied in unenclosed areas that inherently are subject to exposure to dust, random smoke or other foreign particulates. An important distinction between such prior art particulate-indicating systems and the present invention is that many thermo-particulate indicating systems are not suitable for use in an environment that exposes humans to the type of particulates that are necessarily emitted from such a monitored insulator coating. On the other hand, the gaseous vapors emitted from the PFT carrier compositions of the present invention have been documented as being safe with respect to inhalation and ingestion potential toxicity to humans. A further important distinction between such prior art particulate-indicating systems and the present invention is that many thermo-particulate indicating systems employ a thermo-particulating compound which has a decomposition temperature in the range of 100.degree. C. or greater, whereas the increase in gaseous vapors emitted from the PFT carrier compounds are such that they are readily detectable at the much lower temperatures.
A subsequently issued U.S. Pat. No. 4,204,428 discloses a thermo-particulating coating system in which an attempt is made to compensate for the non-discriminating nature of an associated condensation nucleic counter detector. In that system a thermo-particulate is collected then chemically dissolved, extracted and chemically analyzed for specific chemical components that are indicative of each type of coating used in the monitoring system. A gas chromatograph is used for making the analyzes. Rather than utilize such an inherently complex indicating and monitoring arrangement, the present invention avoids the use of a particulate system entirely, in favor of using readily identifiable essentially particulate free and essentially chemical vapors that are selectively emitted from predetermined compositions as a function of the compositions becoming over-heated at certain critical temperature levels.